Many devices for controlling the spread and the amount of fertilizer or other granular material have been disclosed.
For example, U.S. Pat. No. 2,907,498 which issued Oct. 6, 1959 by Cornelis van der Lely et al discloses a horizontal plate 27 which forms a bottom of the hopper vertical slide 23 which slides along the wall of the hopper. Both plate 27 and slide 23 may be opened or closed by movement imparted by the rotation of axis 32.
A further example is U.S. Pat. No. 3,586,246, also by Cornelis van der Lely et al and issued Jun. 23, 1971. This document relates to a spreading implement with one or more flow control members which are positioned below the container and are movable in a register with the outlet via an adjusting or setting mechanism.
Another spreading implement by Cornelis van der Lely et al may be found in U.S. Pat. No. 3,615,055 which issued Oct. 26, 1971. This U.S. patent document also discloses a hopper with an outlet opening and a flow control member movable relative thereof.
U.S. Pat. No. 4,008,854 of Ary van der Lely et al issued on Feb. 22, 1977, describes a hopper with two outlet ports on the bottom thereof and flow control devices, which have holes, positioned beneath each port.
Described in U.S. Pat. No. 4,183,468, also by Ary van der Lely et al, uncovers the plurality of ports of its spreader via hydraulic control.
U.S. Pat. No. 4,609,153 by Cornelis van der Lely issued Sep. 2, 1986. This U.S. patent describes a spreader with dosing plates in the hopper's bottom having openings which cooperate with one another in an adjustable manner.
Ary van der Lely et al also describe, in U.S. Pat. No. 4,834,296, which issued May 30, 1989, a spreader wherein the size of the aperture of each port is adjustable by a dosing slide.